Method of manufacturing multilayer ceramic wiring board and conductive paste for use

ABSTRACT

The present invention provides a method of manufacturing a low-temperature sintering multilayer ceramic wiring board comprising the steps of: forming a wiring layer by printing conductive paste ( 4 ) on an unfired green sheet ( 1 ); forming a laminate by laminating, on at least one side of a ceramic substrate, the unfired green sheet having the wiring layer; and firing the laminate. The present invention also provides paste for use with this method. In the firing step, after an adhesive layer ( 8 ) or binder resin in said green sheet used for lamination burns, glass ceramic in the green sheet starts to sinter, and upon or after the start of sintering of the glass ceramic, conductive particles in the conductive paste starts to sinter. This manufacturing method can provide an precise wiring board without pattern deformation and also provide a low-temperature ceramic multilayer wiring board that has no cracks in the glass ceramic on the periphery of electrodes and has electrodes of a dense film structure.

FIELD OF THE INVENTION

The present invention relates to a method for manufacturing a multilayerceramic wiring board on which semiconductor LSIs and the like aremounted and wired to each other, and also relates to conductive pastefor use with the wiring board.

BACKGROUND OF THE INVENTION

With recent advances in downsizing and weight reduction of semiconductorLSIs, chip components and the like, downsizing and weight reduction ofwiring boards on which such elements are mounted are also desired. Tomeet such a request, multilayer ceramic wiring boards that allowhigh-density wiring thereon and can be formed thin have becomeincreasingly valued in today's electronics industry.

Methods of manufacturing a multilayer ceramic wiring board are roughlyclassified into two kinds. One method is called multilayer printingmethod, in which insulating layers and conductive layers are printedalternately on a ceramic substrate. Another is called laminating method,in which a plurality of green sheets are laminated and fired.

The multilayer printing method has a problem of short circuits caused byinvolving foreign matters such as a little piece of thread duringprinting. To solve this problem, repeated printing of insulating pasteto thicken insulating layers is performed. However, the operationbecomes more complicated and chances of foreign matters involvingincrease when printing and drying are repeated. Therefore, this is not acomplete solution.

Another solution is using a metal mask or low mesh screen mask to obtaina thick film at one printing operation. However, this method hasproblems such as occurrence of deviations in film thickness anddifficulty of high-density wiring.

On the other hand, with the lamination method, shrinkage of themultilayer ceramic wiring board is involved by a sintering when thelaminate is fired. The shrinkage involved by the sintering vary withboard materials used, compositions of green sheets, lots of particles,and the like. The shrinkage poses several problems in production of amultilayer wiring board.

Firstly, because inner layer wiring in a green sheet laminate are firedbefore forming wiring on a uppermost layer, a high degree ofplane-directional shrinkage of the board material hinders connectionbetween patterns on the uppermost wiring and electrodes on the innerlayer. As a result, a land of unnecessarily large area must be formedfor electrodes on the uppermost layer so as to allow the shrinkageerror. Therefore, such lamination method is difficult to be used forhigh-density wiring. To solve this problem, in some cases, a largenumber of screen masks for the wiring on the uppermost layer areprepared according to degrees of shrinkage and used according toshrinkage rates of the wiring board. This solution requires a largenumber of screen masks and is uneconomical.

If the wiring on the uppermost layer are fired with the inner layer atthe same time, such a large land is unnecessary. However, with thissimultaneous firing method, shrinkage of the wiring board still exists.As a result, in some cases, cream solder cannot be printed on requiredpositions of the multilayer ceramic wiring board, in printing the creamsolder for mounting components thereon. In addition, when components aremounted on the wiring board, the shrinkage causes displacement betweenthe components and their predetermined positions.

In order to minimize such shrinkage error, it is necessary tosufficiently control not only substrate materials and green sheetcompositions but also difference in particle lots and laminationconditions (press pressures and temperatures) during manufacturingprocess. However, it is said that deviation of approx. ±0.5% inshrinkage exists.

This problem resulting from shrinkage is not only of multilayer wiringboards but also is common to sintering of ceramics and glass ceramics.

Japanese Patent Laid-Open Publication No. H05-102666 discloses thefollowing method. When a low-temperature sintering glass ceramiclaminate is fired, a green sheet including inorganic fine particles thatdo not sinter at a sintering temperature of glass ceramiclow-temperature sintering material is attached to at least one face ofthe low-temperature sintering glass ceramic laminate In the followingdescription, “sintering” means not only simple sintering of crystals butalso include a binding by a melting of glass components. In this method,after the laminate is fired, the inorganic fine particles are removed.As a result, the low-temperature sintering materials are sintered onlyin the thickness direction and a wiring board having noplane-directional shrinkage is produced. Consequently, the above problemresulting from the shrinkage of the wiring board involved by firing canbe solved.

However, the above method for producing a wiring board requires a greensheet of inorganic fine particles other than glass ceramic green sheets.In addition, a process of removing non-sintering inorganic fineparticles from the wiring board after firing is necessary.

DISCLOSURE OF THE INVENTION

The present invention is a method of manufacturing a low-temperaturefiring multilayer ceramic wiring board comprising the steps of:

forming a wiring layer by printing conductive paste on an unfired greensheet;

forming a laminate by laminating, on at least one face of a ceramicsubstrate, the unfired green sheet having the wiring layer formedthereon; and

firing the laminate.

This method allows sintering of the board materials only in thethickness direction and production of a wiring board having noplane-directional shrinkage. Moreover, the sintered ceramic board itselfcan be used as a part of wiring board and such a step as removinginorganic fine particles can be eliminated.

The present invention is characterized by timing sintering of the greensheet to sintering of electrode (conductor) material in the followingmanner:

in the firing step, after binder resin in the green sheet burns out,glass ceramic in the green sheet starts to sinter, and upon or after thestart of sintering of the glass ceramic, conductive particles in theconductive paste starts to sinter.

In other words, when sintering of the green sheet is not timed tosintering of electrode (conductor) material, the conductor materialsinters earlier than the start of sintering of the board materialsduring firing, for example, and this causes cracks in the substrate onthe periphery of electrodes after firing. For this reason, when theabove multilayer wiring board having less plane-directional shrinkage isused, such conductive paste appropriate for the board is necessary.

The above manufacturing method in accordance with the present inventioncan provide an accurate wiring board without pattern deformation. Thewiring board has no cracks in glass ceramic on the periphery ofelectrodes and has electrodes of a dense film structure.

The present invention is also characterized by further including a stepof forming a second wiring layer on at least one face of a ceramicsubstrate prior to a lamination of the green sheet and the ceramicboard. This step can prevent short circuits between wiring layers, whichis one of the largest problem of a multilayer ceramic wiring board madeby the conventional printing lamination method, and also provide amultilayer ceramic wiring board having high dimensional accuracy and nowarp.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional view showing a manufacturingprocess of a multilayer ceramic wiring board in accordance with a firstembodiment of the present invention,

FIG. 2 is a cross sectional view of a multilayer ceramic wiring board inaccordance with a ninth embodiment of the present invention, and

FIG. 3 is a cross sectional view of a multilayer ceramic wiring board inaccordance with a tenth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A manufacturing process in accordance with the present inventionincludes the following steps.

Firstly, wiring patterns are printed on an unfired green sheetcontaining at least ceramic powder and glass as a main component,plasticizer and solvent, using conductive paste.

Next, the printed unfired green sheet is laminated on at least one faceof a fired ceramic substrate. There are two lamination methods: one isusing adhesive material and another is using a resin component containedin the green sheet. The number of green sheets to be laminated is atleast one. Laminating a large number of green sheets as required canmanufacture a laminate having a large number of lamination.

In the lamination, heat press bonding at a temperature of at least 70°C. can laminate the unfired green sheet onto the ceramic substrateuniformly. In addition, use of thermoplastic resin as a main componentof the adhesive layer improves the adhesion property to the ceramicsubstrate and can provide an excellent multilayer wiring board withoutdelamination of the laminated layers.

Thereafter, a multilayer ceramic wiring board having a large number oflamination can easily be manufactured by firing the laminate.

In the firing process, during or after burnout of the adhesive layer orresin, glass ceramic in the green sheet starts to sinter. Moreover, uponor after the start of sintering of the glass ceramic, the conductiveparticles in the conductive paste starts to sinter.

With the above method, the glass ceramic and conductive particles cansinter irrespective of softening, firing, and removing steps of theadhesive layer. As a result, an accurate wiring board without patterndeformation can be obtained.

In addition, the conductive particles in the conductive paste start tosinter upon or after the start of sintering of the glass ceramic. Thisstep can provide a multilayer wiring board that has no cracks in glassceramic on the periphery of electrodes and has electrodes of a densefilm structure.

The conductive paste for use with the present invention is characterizedby containing several kinds of glass frits each having differentsoftening points. Use of the conductive paste of the present inventionrenders a function of adhering to the ceramic substrate and a functionof having a sintering behavior timed to sintering of the green sheet,during firing of the conductive paste.

The green sheet for use with the present invention is characterized inthat its glass ceramic particles start to sinter at a temperatureranging from 600° C. to 700° C. The composition of the green sheetallows the glass ceramic to start sintering after the organic binder inthe adhesive layer or conductive paste is removed. Because factors thathinder the sintering are removed in this manner, excellent sinteringcondition is obtained at a low sintering temperature of 900° C.

Hereinafter described are specific embodiments of the present invention.

First Embodiment

A method of manufacturing a multilayer ceramic wiring board inaccordance with a first embodiment of the present invention ishereinafter described with reference to the accompanying drawings.

FIG. 1(a) is a schematic drawing showing a step of printing conductivepaste on a green sheet using a screen mask in a process of manufacturinga multilayer ceramic wiring board in accordance with the firstembodiment of the present invention. FIG. 1(b) is a schematic drawingshowing that an adhesive layer of thermoplastic resin is formed on aceramic substrate. FIG. 1(c) is a schematic drawing showing a step oflaminating the green sheet on the ceramic substrate. FIG. 1(d) shows aschematic drawing of a multilayer wiring board after firing.

A method of forming the multilayer board is described below.

Firstly, conductive paste 4 is printed on unfired glass ceramic greensheet 1 using screen mask 2 and squeegee 3 to form patterned conductor5. The glass ceramic materials contained in the green sheet starts tosinter at a temperature of 600° C. In the conductive paste,silver/platinum alloy particle of 4.0 μm in diameter is used, as aconductor, and glass frits having softening temperatures of 625° C. and785° C. are added thereto. The paste contains a plurality of resincomponents, which are burned and removed at temperatures ranging from200° C. to 380° C.

Next, adhesive layer 8 of thermoplastic resin is formed on ceramicsubstrate 6 using ceramic squeegee 7. As the adhesive layer, athermoplastic resin to be completely removed at a temperature of 450° C.is used.

Next, green sheet 1 having patterned conductor 5 formed thereon islaminated on ceramic substrate 6 having adhesive layer 8 formed thereon,and is heat press bonded to form laminate 9. The heat press bondingtemperature is 130° C.

Next, the laminate is fired according to a firing profile (peaktemperature: 900° C., ten minutes, and period of time from take-in totake-out: one hour) to obtain multilayer ceramic wiring board 10.

In accordance with this embodiment, after combustion of the adhesivelayer or binder resin, the glass ceramic materials in the green sheetstarts to sinter, and then the conductive particles in the conductivepaste sinter. For this reason, the glass ceramic materials andconductive particles can sinter irrespective of softening and removal ofthe adhesive layer. As a result, an accurate wiring board withoutpattern deformation can be obtained. In addition, the conductive pasteis designed so that sintering of the conductive particles is timed tothe start of sintering of the glass ceramic. This paste can providewiring board that has no cracks on the periphery of electrodes and hasconductors of a dense film structure.

In this embodiment, the adhesive layer is formed using a ceramicsqueegee; however, the present invention is not limited to the use ofthe ceramic squeegee. The adhesive layer can be formed by dipping,spraying, printing, or the like.

Second Embodiment

The conductive paste in accordance with the present invention isdescribed below. The steps of pattern formation and firing are the sameas those of first embodiment.

The glass ceramic materials contained in the green sheet used in thisembodiment starts to sinter at a temperature of 650° C. In theconductive paste, gold particle of 3.2 μm in diameter is used, as aconductor, and glass frits having softening temperatures of 480° C. and860° C. are mixed and added thereto. Table 1 shows a temperature rangein which resins in the pastes are removed. In other words, in thisembodiment, a plurality of pastes having different combinations ofresins are used as shown in Table 1.

For each of the pastes, the cross section of the conductor is comparedthrough observation of the cross section of the multilayer wiring board.According to the comparison, in each of pastes A and B, sintering of theconductor is proceeding; however, pattern deformation after firing isdeveloped.

Each of pastes F and G results in poor sintering condition and was notappropriate for an electrode pattern of high-density wiring. Amongthese, each of pastes C, D, and E has no pattern deformation afterfiring and results in dense electrode condition. Especially, paste D,which has a temperature range of 200° C., has the best electrode surfacecondition.

The above results show that the conductive paste that contains aplurality of resin components burned and removed at temperatures rangingfrom 140° C. to 250° C. during firing process is the best. It is assumedthat removal of a plurality of resin components in paste in anappropriate duration and within a wide temperature range can delay thestart of sintering of the conductive particles and thus an accuratepattern without deformation can be formed irrespective of the binderresin or adhesive layer.

Third Embodiment

Another conductive paste in accordance with the present invention isdescribed below. The steps of pattern formation and firing in thisembodiment are the same as those of the first embodiment.

The glass ceramic material contained in the green sheet used starts tosinter at a temperature of 615° C. In the conductive paste, silverpalladium particle of 2.0 μm in diameter is used, as a conductor. Aglass frit having a softening point of 510° C. is added, as a lowsoftening point glass frit, and a glass frit having various softeningtemperatures as shown in Table 2 is added, as a high softening pointglass frit. In this embodiment, a plurality of pastes having differentcombinations of glass frits are prepared. A plurality of resincomponents contained in the pastes are removed within a temperaturerange of 220° C. to 360° C.

When the pastes shown in Table 2 were compared with each other, in eachof pastes H and I, cracks resulting from shrinkage of electrodes aredeveloped in the glass ceramic material on the periphery of theelectrodes after firing. Paste N shows poor sintering condition and wasnot appropriate for a high-density electrode pattern. Among these, eachof pastes J to M has no cracks in the glass ceramic material afterfiring and had dense electrode condition. Especially, paste K, whichuses a glass frit having a softening temperature of 790° C., shows thebest electrode condition.

The above results show that setting the softening point of the highsoftening glass contained in the conductive paste to a temperatureranging from 760° C. to 870° C. can control sintering condition of theconductor contained in the paste. With the above composition, amultilayer ceramic wiring board without cracks can be produced even whenthe paste and the glass ceramic green sheet are fired simultaneously.

Fourth Embodiment

Another conductive paste in accordance with the present invention isdescribed below. The steps of pattern formation and firing are the sameas those of the first embodiment.

The glass ceramic material contained in the green sheet used starts tosinter at a temperature of 680° C. In the conductive paste, silverparticle of 1.5 μm in diameter is used. A glass frit having a softeningpoint of 760° C. is added, as a high softening point glass flit, and aglass frit having various softening temperatures as shown in Table 3 isadded, as a low softening point glass flit. A plurality of pastes havingdifferent combinations of glass frits are prepared. A plurality of resincomponents contained in the pastes are removed at temperatures rangingfrom 220° C. to 440° C.

When the pastes shown in Table 3 are compared with each other, in eachof pastes O and P, cracks are developed in the glass ceramic material onthe periphery of electrodes after firing. In each of pastes U and V,delamination is developed between the alumina substrate and theelectrodes. Among these, each of pastes Q to T has no cracks in theglass ceramic material after firing and has excellent adhesion to thealumina substrate. Especially, paste S, which uses a glass frit having asoftening temperature of 600° C., shows the best electrode condition.

The above results show that softening of the glass frit contained in theconductive paste at temperatures ranging from 450° C. to 650° C. iseffective in rendering excellent adhesion between alumina substrate andthe conductor. The results also show that an excellent multilayerceramic wiring board can be produced because sintering of the conductiveparticles is not hastened more than required in the above composition,and thus no cracks occur in the glass ceramic material.

Fifth Embodiment

A fifth embodiment of the present invention is described below.

In the conductive paste of this embodiment, silver particle of 6.0 μm indiameter is used, and a glass frit having a particle diameter of 5.5 μmand a softening temperature of 625° C. is used. A plurality ofconductive pastes to which different amounts of the glass frit are addedare prepared and compared with each other as shown in Table 1. Thecomposition of the paste is shown in Table 4.

The steps of pattern formation and firing in this embodiment are thesame as those of the first embodiment.

The pastes are compared with each other through observation of the crosssections of the wiring boards. According to the comparison, in paste A,sintering of the conductor is proceeding; however, cracks were developedin the glass ceramic layer. Each of paste G and H had poor sinteringcondition and are not appropriate for an electrode pattern ofhigh-density wiring. Among these, each of pastes B to F has no cracks inthe glass ceramic layer after firing and had dense electrode condition.Especially, paste C, which has 3 wt. % of grass frit, shows the bestelectrode condition.

The above results show that the conductive paste having 92.0 wt. % to98.5 wt. % of conductive component, 1.5 wt. % to 8.0 wt. % of glasscomponent can provide wiring that has no cracks in the glass ceramiclayer on the periphery of electrodes and has electrodes of a dense filmstructure.

Sixth Embodiment

The conductive paste of this embodiment is described below.

The steps of pattern formation and firing in this embodiment are thesame as those of the fifth embodiment.

In the conductive paste of this embodiment, gold particle of 8.0 μm indiameter is used, and 4.0 wt. % of glass frits of 6.2 μm in particlediameter is added thereto. The softening temperatures of the glass fritsused are shown in Table 5. As shown in Table 5, a plurality of pasteshaving different softening temperatures glass flits are prepared.

The pastes are compared with each other through observation of the crosssections of the multilayer wiring boards. According to the comparison,in paste I, sintering of the conductor is proceeding; however, cracksare developed in the glass ceramic layer. With each of pastes O and P,cracks are developed in the glass ceramic layer. Among these, each ofpastes J to N has no cracks in the glass ceramic layer and has denseelectrode condition. Especially, paste K, which has a glass frit havinga softening temperature of 465° C., shows the best electrode condition.

The above results show that setting the softening temperatures of glassfrits used in the conductive paste from 400° C. to 650° C. allows theglass to soften at low temperatures, to enter between the conductor andalumina substrate, resulting in a close contact between them. And, thus,friction between the conductor and the alumina substrate inhibits thesintering shrinkage of the conductor. Consequently, cracks resultingfrom shrinkage of electrodes can be prevented.

Seventh Embodiment

The conductive paste of this embodiment is described below.

The steps of pattern formation and firing in this embodiment are thesame as those of Fifth Embodiment.

In the conductive paste of this embodiment, silver/palladium particle of8.5 μm in diameter is used, and 7.0 wt. % of a glass frit having asoftening temperature of 575° C. are added thereto. The particlediameters of the glass frits used are shown in Table 6. As shown in thetable, a plurality of pastes having different particle diameters areprepared.

When the pastes are compared with each other, in each of pastes Q and R,cracks resulting from shrinkage of electrodes are developed in the glassceramic layer on the periphery of the electrodes after firing. Also ineach of pastes W and X, cracks are developed in the glass ceramic layer.Among these, each of pastes S to V shows no cracks in the glass ceramiclayer after firing and has dense electrode condition. Especially, pasteU, which has a glass frit of 7 μm in particle diameter, shows the bestelectrode condition.

The above results show that setting the particle diameter of the glassfrit from 5.0 to 8.0 μm allows firing without promoting sinteringshrinkage of conductive particles even when a glass having a lowsoftening temperature is used, and thus prevents cracks resulting fromshrinkage of the electrodes.

Eighth Embodiment

The conductive paste of this embodiment is described below.

The steps of pattern formation and firing in this embodiment are thesame as those of fifth embodiment.

In the conductive paste of this embodiment, silver/platinum alloy isused, and 4.0 wt. % of glass frit having a softening temperature of 400°C. and a particle diameter of 8.0 μm is added. The particle diameters ofthe conductive particles added to the pastes are shown in Table 7. Asshown in the table, a plurality of pastes having different particlediameters are prepared.

When the pastes were compared with each other, in each of pastes Y andZ, cracks are developed in the glass ceramic layer on the periphery ofthe electrodes after firing. Each of pastes AF and AG has poor sinteringcondition and is not appropriate for an electrode pattern ofhigh-density wiring. Among these, each of pastes AA to AE has no cracksin the glass ceramic layer after firing and has dense and excellentelectrode condition. Especially, paste AC, which has a particle diameterof 8.0 μm, has the best electrode condition.

The above results show that setting the particle diameter of theconductive particles from 6.0 μm to 10.0 μm can inhibit sinteringshrinkage of conductive particles in firing of the conductive paste, andthus prevent cracks in the glass ceramic layer resulting from shrinkageof the electrodes.

In the above description, specific numeric values are provided; however,when the conductive paste has the following composition, excellentresults can be obtained.

-   (1) Conductive component: 92.0 wt. % to 98.5 wt. % and    -   Glass component: 1.5 wt. % to 8.0 wt. %-   (2) Softening temperature of at least one glass frit: 400 (450) ° C.    to 650° C.,    -   Softening temperature of at least one other glass frit: 760° C.        to 870° C. and    -   Particle diameter of the glass frit: 5.0 μm to 8.0 μm-   (3) Diameter of conductive particles in the conductive paste: 1.0 μm    to 10.0 μm-   (4) A plurality of resin components contained in the conductive    paste are burned out within a temperature range of 140° C. to    250° C. and a plurality of resin components contained in the    conductive paste are burned out at temperatures ranging from 200° C.    to 450° C.

Setting the diameter of the conductive particles from 1.0 μm to 10.0 μmas described above can prevent sintering of the conductive particlesfrom being hastened more than required and thus adjust a timing ofsintering of the conductive particles to sintering of the glass ceramicmaterials in the green sheet.

While silver, silver palladium, silver/platinum, or gold is used as aconductive component in this embodiment, the same result can be obtainedwith a paste containing at least one selected from copper, silver,silver palladium, silver platinum and gold.

Moreover, when an adhesive layer and resin layer that can be removed ata temperature up to 450° C. is used, an accurate electrode pattern canbe produced as well.

In other words, by using an adhesive layer and resin layer that can beremoved at a temperature up to 450° C., the resin components areeliminated when the green sheet and the conductive paste are sintered,and thus they can be bonded to the ceramic substrate well.

The green sheet is laminated onto the ceramic substrate at a temperatureof 130° C. in the first embodiment. However, heat press bonding at atemperature of at least 70° C. is applicable as well. At a temperaturebelow 70° C., dense lamination cannot be made and delamination occursduring firing.

While sintering of the glass ceramic particles in the green sheet attemperatures of 600, 615, 650 and 680° C. is described in thisembodiment, an accurate multilayer ceramic wiring board can bemanufactured as well when the sintering starts at any temperatureranging from 600° C. to 700° C.

Ninth Embodiment

A method of manufacturing a multilayer ceramic wiring board inaccordance with this embodiment is hereinafter described with referenceto the accompanying drawings. FIG. 2 is a cross sectional view of amultilayer ceramic wiring board in accordance with this embodiment.

First, wiring layers 22 are screen-printed on green sheet 23 usingsilver paste and dried beforehand. Successively, unfired green sheet 23are overlaid on alumina substrate 21 and then heat press bonded attemperatures ranging from 50° C. to 150° C. and at a pressure rangingfrom 5 kg/cm² to 50 kg/cm² to bond ceramic substrate 21 and green sheet23.

Green sheet 23 is obtained by kneading a low-temperature firing glassceramic component comprising boro-silicated glass powder and aluminapowder with an organic binder to form slurry and applying the slurryusing doctor blade method and the like. In this embodiment, a greensheet having a film thickness of 10 μm after firing is used. In bondingto the substrate, applying a thermoplastic or thermosetting resin overthe surface of alumina substrate21 and then performing heat pressbonding of green sheet 23 can provide more completely bonded condition.

Next, wiring layers 24 are formed on the bonded unfired green sheet 23using silver paste and then fired at temperatures ranging from 850° C.to 1000° C. to obtain a multilayer ceramic wiring board.

The insulation resistance between the each of the wiring layers obtainedin this embodiment are measured. No short circuits are observed and avery high insulation resistance of at least 10¹³Ω is obtained betweenthe wiring layers. When the thickness between wiring layers is 10 μm,incidence of short circuits is so high as 80% with the conventionalthick film printing method. In contrast, with the method in accordancewith the present invention, no short circuit is observed and a highlyreliable multilayer ceramic wiring board can be obtained.

While only one layer of green sheet is press bonded to the substrate inthis embodiment, the same result can be obtained when a desired numberof green sheets having wiring layers using silver paste are laminated.

Tenth Embodiment

A method for manufacturing a multilayer ceramic wiring board inaccordance with this embodiment is hereinafter described with referenceto the accompanying drawings. FIG. 3 is a cross sectional view of amultilayer ceramic wiring board in accordance with this embodiment.

Through holes are formed in positions of sintered alumina substrate 31where electrical connections between front and back faces are desired,using CO₂ laser. After the formation of the through holes, the throughholes were filled with silver/palladium paste and fired to form throughholes 36.

Next, through holes are made in required positions of green sheet 33using a puncher to form via holes. Then, the via holes are filled withsilver/palladium paste and dried to form via 35. Thereafter, wiringlayer 32 is screen-printed on green sheet 33 having via 35 and dried.

Successively, green sheet 33 is overlaid on alumina substrate 31 andthen heat press bonded at temperatures ranging from 50° C. to 150° C.and pressures ranging from 5 kg/cm² to 50 kg/cm² to bond fired ceramicsubstrate 31 and green sheet 33.

Green sheet 33 is produced in a manner similar to that of the ninthembodiment. Also, the effect of the thermoplastic or thermosetting resinin bonding is the same as that of the ninth embodiment.

Next, wiring layer 34 is formed on green sheet 33 after the bonding,using silver paste, and thereafter they are fired at temperaturesranging from 850° C. to 1000° C. to obtain a multilayer ceramic wiringboard.

Successively, backside wiring layer 37 is screen-printed on substrate 31on a opposite face of the green sheet lamination, using conductivepaste, in a manner so that the back face wiring is connected to throughhole 32, and fired be obtain a multilayer wiring board having wiringlayers on both faces.

The insulating resistance between each of the wiring layers of thewiring board obtained in this embodiment is also so high as at least10¹³Ω and a highly reliable wiring board having wiring layers on bothfaces can be obtained.

While only one layer of green sheet is press bonded in this embodiment,a multilayer ceramic wiring board can be obtained when a desired numberof green sheets each having via and a wiring layer made using silverpaste are laminated to provide multiple layers. In addition, in thisembodiment, a screen printing method is used for the formation of backface wiring layer 37. However, the same result can be obtained and amore precise pattern can be formed using the intaglio transfer printingmethod.

While back face wiring are printed after firing of the green sheet inthis embodiment, they can be printed prior to firing of the green sheet,followed by a simultaneous firing of wiring on both faces.

In addition, it is also possible to print wiring pattern on at least oneface of the substrate prior to green sheet lamination, followed by asimultaneous firing of the green sheet and the wiring pattern.

The features of this embodiment are as follows:

(1) Because a sintered ceramic substrate is used as a base materialinstead of a green sheet in the green sheet lamination method, amultilayer wiring board without warp and with high dimensional accuracycan be obtained.

(2) A multilayer ceramic wiring board having a desired number oflamination, no deviations in film thickness and no pores can be obtained

(3) Electrical conduction between neighboring wiring layers laminatedcan be obtained at any desired positions. Therefore, a high degree offreedom in pattern designing can be obtained and a downsizedhigh-performance multilayer wiring board can be manufactured.

(4) Green sheets can be laminated onto a fired ceramic substrateuniformly.

(5) Because sintering of the green sheet is completed at a relativelylow temperature, influence on other components such as electrodes thathave already been provided on the board can be reduced. Further, thestructure makes it possible to use materials having properties differentfrom those of electrodes on the inner layer, for electrodes on theoutermost layer. This can add migration resistant property or the likeproperties, which improve the degree of freedom in design.

(6) Through holes allow electrical connection between front and backfaces of the ceramic substrate at any desired position. This renders ahigher degree of freedom in designing patterns and in manufacturing of adownsized high-performance multilayer wiring board. Moreover, amultilayer ceramic wiring board having excellent electricalcharacteristics and electrical conduction with a low resistance can bemanufactured.

INDUSTRIAL APPLICABILITY

As described above, in accordance with the present invention, an precisewiring board without pattern deformation can be produced. This isbecause after combustion of resin components, glass ceramic starts tosinter and successively conductive particles in conductive paste sinter,in firing of a low-temperature multilayer ceramic wiring board. Inaddition, upon or after the start of sintering of the glass ceramic, theconductive particles in the conductive paste start to sinter. Thus, alow-temperature multilayer ceramic wiring board that has no cracks inthe glass ceramic layer on the periphery of electrodes and haselectrodes of a dense film structure can be manufactured.

TABLE 1 Paste No. A B C D E F G Firing 70 110 140 200 250 270 300temperature range

TABLE 2 Paste No. H I J K L M N Softening 700 740 760 790 830 870 900temperature

TABLE 3 Paste No. O P Q R S T U V Softening 400 430 450 500 600 650 680700 temperature

TABLE 4 Paste No. A B C D E F G H Glass 0.5 1.5 3.0 5.0 7.0 8.0 8.5 9.0composition Conductor 99.5 98.5 97.0 95.0 93.0 92.0 91.5 91.0compositionUnit of Composition: Wt. %

TABLE 5 Paste No. I J K L M N O P Softening 380 400 465 510 595 650 675710 temperature

TABLE 6 Paste No. Q R S T U V W X Glass particle 3 4 5 6 7 9 9 10diameterUnit of Glass Particle Diameter: μm

TABLE 7 Paste No. Y Z AA AB AC AD AE AF AG Conductive 4 5 6 7 8 9 10 1112 particle diameterUnit of Conductive Particle Diameter: μm

1. A method of manufacturing a multilayer ceramic wiring boardcomprising the steps of: forming a wiring layer by printing conductivepaste on an unfired green sheet; forming an adhesive layer on at leastone face of a ceramic substrate, said adhesive layer comprising one of athermoplastic resin and a thermosetting resin as a main component;forming a laminate by laminating said unfired green sheet having saidwiring layer on said face of the ceramic substrate; firing said laminateso as to remove a binder resin in said green sheet and said adhesivelayer; and sintering glass ceramic materials in said green sheet andconductive particles in said conductive paste onto said face of theceramic substrate, wherein, after a burnout of said binder resin, saidglass ceramic materials start to sinter, and one of upon and after startof sintering of said glass ceramic materials, said conductive particlesstart to sinter, wherein said conductive paste includes a plurality ofresin components, each of the resin components has a burn-outtemperature range having a variation of 140° C. to 250° C., and saidplurality of resin components are burned out at a temperature of 200° C.to 450° C.
 2. The method for manufacturing a multilayer ceramic wiringboard according to claim 1 wherein, heat press bonding is performed at atemperature of at least 70° C. in said lamination step.
 3. The method ofmanufacturing a multilayer ceramic wiring board according to claim 1wherein said conductive paste includes 92.0 wt. % to 98.5 wt. % ofconductive component and 1.5 wt. % to 8.0 wt. % of inorganic bindercomponent.
 4. The method of manufacturing a multilayer ceramic wiringboard according to claim 1 wherein said conductive paste includes aplurality of kinds of glass frits, each having different softeningpoints.
 5. The method of manufacturing a multilayer ceramic wiring boardaccording to claim 1 wherein at least one kind of glass frit in saidconductive paste has a softening temperature ranging from 760° C. to870° C.
 6. The method of manufacturing a multilayer ceramic wiring boardaccording to claim 1 wherein at least one glass frit in said conductivepaste has a softening temperature ranging from 450° C. to 650° C.
 7. Themethod of manufacturing a multilayer ceramic wiring board according toclaim 1 wherein a particle diameter of a glass frit used in saidconductive paste ranges from 5.0 μm to 8.0 μm.
 8. The method ofmanufacturing a multilayer ceramic wiring board according to claim 1wherein said adhesive layer is removed at a temperature up to 450° C. 9.The method of manufacturing a multilayer ceramic wiring board accordingto claim 1 wherein said conductive paste includes conductive particleshaving a diameter ranging from 1.0 μm to 4.0 μm.
 10. The method ofmanufacturing a multilayer ceramic wiring board according to claim 1wherein said conductive paste includes conductive particles having adiameter ranging from 6.0 μm to 10.0 μm.
 11. The method of manufacturinga multilayer ceramic wiring board according to claim 1 wherein saidconductive paste includes, as a conductive component, at least oneselected from a group consisting of copper, silver, silver palladium,silver platinum, and gold.
 12. The method of manufacturing a multilayerceramic wiring board according to claim 1 wherein glass ceramicparticles in said green sheet start to sinter at a temperature rangingfrom 600° C. to 700° C.
 13. The method of manufacturing a multilayerceramic wiring board according to claim 1 further comprising a step offorming a second wiring layer on at least one face of said ceramicsubstrate prior to said lamination.
 14. The method of manufacturing amultilayer ceramic wiring board according to claim 13 wherein aplurality of unfired green sheets each having said wiring layer thereonare laminated to provide multiple layers.
 15. The method ofmanufacturing a multilayer ceramic wiring board according to claim 14wherein said unfired green sheet has at least one via hole forelectrical connection between wiring formed on said plurality of unfiredgreen sheets.
 16. The method of manufacturing a multilayer ceramicwiring board according to claim 13 wherein said ceramic substrate has atleast one through hole.
 17. The method of manufacturing a multilayerceramic wiring board according to claim 16 wherein an inside of saidthrough hole is filled with a conductor.
 18. The method of manufacturinga multilayer ceramic wiring board according to claim 1 wherein saidwiring layer is formed using an intaglio transfer printing method. 19.The method of manufacturing a multilayer ceramic wiring board accordingto claim 1 wherein the step of firing said laminate so as to remove saidadhesive layer causes at least a portion of respective surfaces of saidceramic substrate and said green sheet to come into contact with eachother.
 20. The method of manufacturing a multilayer ceramic wiring boardof claim 1, wherein binder resin in said conductive paste is burned andremoved at temperatures ranging from 200° C. to 380° C.